Hello DeniseB52,
Thank you for reaching out to Constant Contact API Developer Support. My team is here to assist outside software developers with questions about building into Constant Contact's API.
It looks like we'll need some additional information in order to assist with troubleshooting. If you could please provide us with the API key that you’re using, a full example campaign scheduling request, including headers, and any timestamps or general timeframes you may have from previous failed requests, we'll be able to better assist in pinpointing the cause of the 400 error response that you’ve encountered. Please provide this information securely by reaching out to us via email at webservices@constantcontact.com, we look forward to assisting you!
Please have a look and let us know if you have any other questions!
Regards,
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